1. Field of the Invention
The present invention relates to semi-conductor wafer handling equipment and, more particularly, to an improved clip and method for securing a semi-conductor wafer to the surface of a support pedestal.
2. History of the Prior Art
In the manufacture of semi-conductor devices, such as integrated circuits, a plurality of devices are generally formed on a single circular wafer of silicon material. The wafer is typically circular in shape and on the order of 6 inches in diameter. The wafers are put through a number of sequential processing steps, including coating them with photo-resists, exposing them to the optical patterns formed on photo masks, and exposing them to both liquid and gaseous treating environments.
The processing of a silicon wafer containing a plurality of semi-conductor devices requires a high degree of cleanliness and sterility in the environment in order to produce acceptable devices. The ability of a semi-conductor device to perform satisfactorily from both an electrical and mechanical standpoint depends upon the nature and quality of the materials forming the various layers of the device. The chemical composition of these materials must be extremely pure. The introduction of any foreign matter into the environment where the wafers are being processed results in a decrease in the "yield" of the wafer. The yield is the number of devices that can pass the required electrical tests of the device after the processing has been completed. This is usually expressed as a fraction of the total number of devices processed on the wafer that did pass the required tests. Thus, the higher the purity of the processing environment and processing techniques used in manufacturing the semi-conductor devices, the greater the yield and hence the greater the financial return to the manufacturer.
Semi-conductor wafers are conventionally exposed to liquid and gaseous treating environments by positioning them within a sealed chamber conventionally referred to as an "etcher." All outside contaminants are excluded from the environment within the etcher which is used to simultaneously expose a plurality of wafers being processed to various gases and/or liquids during the wafer processing operation. One type of semi-conductor wafer processing etcher includes, within the sealed chamber, a hexagonal column referred to as a "hexode". The hexode has a plurality of vertically extending planar sidewalls, and attached to each sidewall are a plurality of support "pedestals." A semi-conductor wafer being processed is attached to such a pedestal and held there by means of wafer retaining clips mounted therearound.
The interior of a typical hexode contains cooling coils for removing heat from the back side of the highly conductive support pedestals and, hence, from the semi-conductor wafers which they support. The back side of each wafer is held flush against the flat upper surface of a pedestal to provide a good heat transfer engagement therebetween in order to cool the wafer and keep the temperature gradients across its surface uniform during processing. It is important that the many different semi-conductor devices being simultaneously formed on the front surface of the wafer each be exposed to the same temperatures and chemicals for identical periods of time in order to ensure uniformity of electrical operating characteristics in each device.
At the end of a processing cycle, the sealed chamber of the etcher is opened and a robotic manipulator is used to depress the latches on the wafer retaining clips and grip the silicon wafers by their edges to remove them from the mounting surface of the pedestals and transfer them to their next processing operation.
To guard against the introduction of impurities into the silicon wafer processing environment, the equipment operators preferably wear caps, gowns, and surgically sterile rubber gloves when they are handling any of the equipment associated with the wafers. In addition, the operators also frequently change gloves, sometimes three to four times per day, to reduce the amount of contaminants which might accumulate thereon and affect the wafer processing environment. Despite all of these precautions, it has been found that the interior of the etchers must be cleaned periodically to remove as many potential future contaminants of the wafers as possible. In addition, the equipment within the interior of the etchers is periodically replaced completely because of an accumulation of potential contaminants which invariably come in contact with the wafers and reduce their yield. Because of the expense connected with both cleaning an etcher as well as periodically replacing the interior parts of an etcher, it is highly desirable to attempt to maximize the length of time in which an etcher can operate without either a cleaning or a replacement of its interior parts. For this reason, it is desirable to provide equipment with which the wafers come in contact of the type minimizing the tendency toward wafer contaminant pollution.
It has been found that one of the means by which contaminants are transferred to the wafers is the wafer retaining clips which are disposed around the periphery of the wafer pedestals mounted on the hexode. Even though these clips are relatively clean and simple in design, it has been found that prior art clip designs tend to accumulate contaminating materials. Such contaminants are accumulated during the processing cycle of one particular batch of wafers and then passed on to a second batch of wafers when they are introduced into the etcher. It has also been found that the specific geometric configuration of the pedestal clips has a relationship to the number of contaminants it collects and in the way in which those contaminants may be passed on to other batches of semi-conductor wafers.
It would, thus, be desirable to provide an improved pedestal retention clip for securing semi-conductor wafers to pedestal surfaces which minimizes the contamination of wafers. The clips should also be quickly and easily detachable from the edge of the semi-conductor wafer and should be easily actuatable by a robotic tool.